Can You Solve the Airplane Fuel Riddle?

Here's a fun riddle: Professor Fukanō plans to circumnavigate the world in his new airplane. But the plane's fuel tank doesn't hold enough for the trip—in fact, it holds only enough for half the trip. But with the help of two identical support planes (which can refuel him in mid-air) piloted by his assistants Fugori and Orokana, the professor thinks he can make it in one trip. But since all three planes have the same problem of limited fuel, how can they work together to achieve the professor's goal without anyone running out of fuel?

Christmas trees aren't for everyone. Some people can't fit a fir inside their cramped abodes, while others are turned off by the expense, or by the idea of bugs hitchhiking their way inside. Fake trees are always an option, but a new trend sweeping Instagram—pineapples as mini-Christmas "trees"—might convince you to forego the forest vibe for a more tropical aesthetic.

As Thrillist reports, the pineapple-as-Christmas-tree idea appears to have originated on Pinterest before it, uh, ripened into a social media sensation. Transforming a pineapple into a Halloween “pumpkin” requires carving and tea lights, but to make the fruit festive for Christmas all one needs are lights, ornaments, swaths of garland, and any other tiny tchotchkes that remind you of the holidays. The final result is a tabletop decoration that's equal parts Blue Hawaii and Miracle on 34th Street.

In need of some decorating inspiration? Check out a variety of “Christmas tree” pineapples below.

Ready to have your mind boggled? Take a look at the image above. What shape are the lines? Do they look like curves, or zigzags?

The image, spotted by Digg, is a new type of optical illusion published in the aptly named journal i-Perception. Discovered by Japanese psychologist Kohske Takahashi, it’s called the “curvature blindness illusion,” because—spoiler—the contrast of the lines against the gray background makes our eye see some of the lines as zigzags when, in fact, they’re all smooth curves.

The illusion relies on a few different factors, according to the three experiments Takahashi conducted. For it to work, the lines have to change contrast just at or after the peak of the curve, reversing the contrast against the background. You’ll notice that the zigzags only appear against the gray section of the background, and even against that gray background, not every line looks angled. The lines that look curvy change contrast midway between the peaks and the valleys of the line, whereas the lines that look like they contain sharp angles change contrast right at the peak and valley. The curve has to be relatively gentle, too.